This invention relates generally to highly purified metal free phthalocyanines, methods of preparation thereof, and soluble metal phthalocyanine complexes with polyethers such as glymes and crown ethers, potassium diglyme phthalocyanines and potassium phthalocyanines complexed with crown ethers and the complexation process with diglyme and crown ethers which is more specifically identified hereinafter as well as methods for interconverting metal free and alkali metal diglyme and crown either complexed phthalocyanines.
Metal free phthalocyanine has the basic structure of the following general formula as described in U.S. Pat. No. 3,357,989 fully incorporated herein by reference. ##STR1##
This species can be modified by substitution around the perimeter of the macrocyclic ring, as is well known in the art and the present invention applies to such molecularly substituted phthalocyanines as well as to the basic structure. Illustrative examples of such substituents include halogen, alkyl, nitro, naphthyl, and anthranyl.
Additionally, as described in the U.S. Pat. No. 3,357,989 referenced, it is known that the two hydrogen atoms in the center of the phthalocyanine molecule can be replaced by metals such as copper, for example. Phthalocyanine itself is known to exist in many crystal forms which forms can be distinguished by comparison of their X-ray diffraction pattern and/or infrared spectra. Further, the basic cyan/blue color of the phthalocyanine pigment varies within a range according to the polymorphic form. For example, the beta form is greener in color than the alpha or gamma forms. Various forms of phthalocyanine both metal containing and metal free, additional polymorphs, have been described, for example, in U.S. Pat. No. 3,051,721 (R-form), U.S. Pat. No. 3,160,635 (delta-form) and U.S. Pat. No. 3,150,150 (another delta-form), as well as U.S. Pat. No. 3,357,989 (an x-form phthalocyanine).
Phthalocyanines are prepared from simple molecules by a variety of methods known in the art. Generally, this involves reaction of a precursor containing the contiguous carbon skeleton ##STR2## which either additionally contain nitrogen atoms or to which is externally supplied a source of such nitrogen atoms in a solvent in the presence or absence of catalysts or additional reagents at elevated temperature for varying amounts of time. The general result of such a synthetic procedure is a crude metal-free or metal-containing, substituted or unsubstituted phthalocyanine. Crude chemical products exhibit properties that combine the properties of the name-giving major constituent and those of the contaminants. Depending upon the desired use, the properties conferred upon the bulk chemical by its contaminants may be detrimental, beneficial, or irrelevant. Detrimental properties may be conferred by unknown constituents simply defined as having been created during the process of synthesis. Therefore, it is generally necessary to purify synthetic materials until properties with respect to a standard have been reached. For materials like phthalocyanine, it is then also necessary to obtain the correct polymorphic form in order to assure desired properties.
The main methods for purification of phthalocyanine methods for purification of phthalocyanine are illustrated in U.S. Pat. Nos. 3,357,989 and 2,741,531. The most widely method used today is as described in the '989 patent which method involves subjecting a mixture of alpha and beta metal free phthalocyanines commercially available from the Arnold Hoffman Company, a division of ICI Limited (Monolite Fast Blue GS) to solvent extraction with dichlorobenzene followed by washing with acetone and drying. The pigment is then subsequently dissolved in concentrated sulfuric acid and precipitated in ice and water followed by washing the precipitate with methanol and subsequently drying. This method, known in the art as the acid pasting method uses one of the few solvents that will cause the phthalocyanine pigment to be dissolved, namely concentrated sulfuric acid. However such acid pasting while useful with respect to gross purification for the pigment industry may introduce new impurities into the metal free phthalocyanine being prepared in view of the chemical reactions that are occurring unless specific reaction parameters such as time, temperature and the like are adhered to. Thus, acid pasted materials prepared show a great variance in properties that are most sensitive to small amounts of adventitious contaminants, such as the electrical or photoelectric properties.
It is significant to note that electrical properties of pigments may be influenced by quantities of contaminants that cannot be detected much less be identified by the usual analytical methods. In such a situation, a progressive change in electrical properties as a function of purification steps constitutes the only practical method for determining a change in materials purity.
Methods of purification for most organic compounds include dissolution/crystallization, dissolution/precipitation, extraction, zone refining, distillation, sublimation, and chromatography of various kinds. All these methods have in common that desired molecules are selectively accumulated in one place while undesired (and frequently unspecified) molecules are ommited from the accumulated material. The specific method chosen for a given material depends both on the properties of the main material and on those of the contaminants.
In U.S. Pat. No. 2,741,531, there is described a method for altering the physical state of metal free phthalocyanine pigments for the purpose of transforming such pigments from the solid state into the form of a solution which is not a metal free phthalocyanine pigment in an alocholic solvent with a strongly basic compound of alkali metal, for instance a hydroxide, alkoxide or hydride of sodium or potassium. This patent is primarily directed to a process for altering the state of phthalocyanine pigments for use in dying cellulosic fibers.
Phthalocyanines have a wide range of uses including uses as pigments and paint materials, textile dyestuffs and as photoconductors which are used in electrophotographic imaging systems. One form of phthalocyanine, namely copper phthalocyanine, is well known and is commercially used in oil paints, water paints, oil printing inks, rubber and textile printing inks. The primary utility of the phthalocyanines made in accordance with the present invention would be as a photoconductor in an electrophotographic imaging system and more specifically, as a layer in organic photoreceptor structure or as an organic photoconductor itself. In the layered organic photoreceptor, the phthalocyanine normally functions as a generating material, that is a material that generates both positive and negative charges, somewhat similar to a selenium layer that is commercially used in electrophotographic systems.
Phthalocyanine is a very complex material and difficulties have been encountered in isolating new forms of phthalocyanines as well as discovering methods for preparing such new forms which are simple and economically attractive. Additionally, those methods which are known for preparing phthalocyanine in most instances result in a phthalocyanine that contains impurities and such impurities can have an adverse effect on the particular phthalocyanine or derivative used, particularly when for example, it is employed in an electrophotographic environment. In view of its extremely low solubility in most solvents, very few known methods result in a purified phthalocyanine with the possible exception of the acid pasting method, and even that method produces phthalocyanines which contain some impurities. One of the difficulties encountered in the acid pasting method is that the reagent slowly destroys the molecule of phthalocyanine. This destruction is a function of time and temperature and an exact regimen of these parameters has to be adhered to, as indicated hereinbefore in order to produce material of reproducible properties. Also, it is generally accepted that the sulfuric acid used cannot be totally eliminated even after repeated washings with ammonia for example. Thus, sulfuric acid and various decomposition products of phthalocyanine are contained in the final product and such phthalocyanine has properties too variable to be workable in a reliable xerographic imaging system.
Accordingly, there is a need for new forms of phthalocyanine, methods of preparing such new forms and methods for obtaining purified phthalocyanines which would be useful as pigments, and particularly for electrophotographic systems. Further, there is a need for a method for the preparation of phthalocyanines which is economical, simple and direct and which method will offer predictability, that is, substantially the same results are achieved when repeating the method a number of times. Also, there is a need for a method which will cause the dissolving of the phthalocyanine which method uses more simple economical and less hazardous materials than sulfuric acid as is used in the prior art.